An aircraft wheel and brake assembly typically includes a heat shield disposed between the wheel and brake disks to prevent conduction and radiation to the aircraft wheel of heat energy generated in the brake disks during braking. Excessive temperatures in the aircraft wheel can damage the wheel and the aircraft tire. The heat shield also prevents hot brake material ejected from the brake disks during braking from being slung against the inside of the wheel, which can also damage the wheel and further contribute to excessive temperatures.
An early example of a heat shield is described by U.S. Pat. No. 3,051,528 issued in 1962 to R. R. Rogers. The Rogers heat shield comprises a multitude of curved heat shield sections disposed between adjacent drive keys. More recent examples are described by U.S. Pat. No. 4,017,123 issued in 1977 to Horner et al. and U.S. Pat. No. 4,084,857 issued in 1978 to VanderVeen. These heat shields also comprise curved heat shield sections disposed between adjacent drive keys. The Horner et al. heat shield sections are captive between the drive key caps and ledges formed on the drive keys. The ledges and drive keys are integrally formed with the wheel, which is typical of wheel and brake assemblies having steel disks. Horner et al. states that the heat shield sections could be used with the removable keys presented in Rogers. However, exactly how this would be accomplished is not clear because the Rogers drive keys do not have ledges or drive key caps. The VanderVeen heat shield section is captive between the drive key cap and an additional cap having a pair of wings that extend from either side of the drive key. The drive keys are integrally formed with the wheel, and wings eliminate the need for the ledges of Horner et al. The heat shields described thus far are representative of the technology developed for wheel and brake assemblies having steel brake disks with metallic friction linings.
The advent of carbon/carbon brake disks instigated further development of heat shields. Carbon/carbon brakes generally operate at a much higher temperature than their steel counter-parts, which necessitated further steps to minimize conduction and radiation of heat energy into the aircraft wheel. Most wheel and brake assemblies having carbon/carbon brakes now have removable torque bars that are spaced from the inside of the aircraft wheel, with attachments at both ends. This arrangement minimizes the conductive path from the torque bars to the wheel. Heat shield contact with the torque bars is preferably minimized for the same reasons. In addition, radiation is a major source of heat transfer from carbon/carbon brakes, which necessitates that the heat shield fully encircle the brake disks with minimum holes or breaks that permit direct radiation of heat energy to the aircraft wheel. Conduction is another major source of heat transfer in carbon/carbon brakes, which is minimized by minimizing contact of the torque bars and heat shield with the aircraft wheel. These considerations caused a significant departure from the earlier heat shield technology developed for steel brakes.
According to one prior art approach, a single piece full circle heat shield is attached to the wheel and brake assembly between the wheel and the torque bars. The heat shield is spaced from both the torque bars and the aircraft wheel in order to minimize heat conduction to the heat shield from the torque bars. The heat shield comprises two cylindrical stainless steel sheets spaced from each other, with insulation in between. A heat shield constructed in such manner, though certainly safe and effective, embodies some undesirable characteristics. For example, the shield tends to warp and buckle during use due to thermal expansion and contraction induced by braking cycles. In addition, removing a damaged heat shield generally requires removing all the torque bars from the aircraft wheel assembly.
Another heat shield is described in U.S. Pat. No. 5,002,342 issued in 1991 to Dyko. The Dyko shield comprises a plurality of heat shield sectors that together define a full circle heat shield. The edges of the heat shield are interleaved in a manner that permits relative expansion and contraction of the heat shield sectors induced by thermal gradients. Also, removal of a single heat shield requires only the removal of those torque bars corresponding to that sector. Thus, individual sectors may be removed and replaced as necessary without replacing the entire heat shield. A similar heat shield having sectors connected by hinged edges is described in U.S. Pat. No. 5,236,249 issued in 1993 to Han et al.
Further heat shield improvements are described in U.S. Pat. No. 5,851,056 issued in 1998 to Hyde. The Hyde heat shield comprises individual heat shield sections disposed between adjacent torque bars and elongate heat shield carriers superposing the torque bars and engaging the heat shield sections. With such an arrangement, the heat shield sections are removable without loosening or removing any torque bars.
Although the Hyde heat shield is an effective heat shield, it and similarly designed heat shields exhibit undesirable characteristics. Since the wheel acts as part of the pressure vessel to contain tire pressure, there is limited structure to which the heat shield sections and carriers can be mounted. For example, the heat shield sections and carriers of the Hyde heat shield are mounted at their axially inboard ends to the wheel flange and extend axially into the tube well. To provide support deep within the tube well, the heat shield carriers include resilient bumpers at their axially outboard ends. The resilient bumpers contact the tube well and restrain radial movement of the heat shield carriers and also the heat shield sections engaged by the carriers. During wheel spin up, the heat shield sections and carriers are forced radially outwardly and the resilient bumpers protect the tube well from being scored. However, over time the resilient bumpers have a tendency to degrade, which may cause the heat shield sections and/or carriers to contact and/or abrade the protective coatings of the tube well. Once the protective coating is removed, the wheel is susceptible to corrosion which can lead to the wheel being prematurely removed from service.
In addition to solving the problem of wheel scoring by other than the use of a bumper that is subject to degradation, there is a general need for further improvements in heat shield systems that provide for easier assembly and withdrawal of individual heat shield sections and/or improved performance of the heat shield.